Another study that challenges the benefits of intermittent fasting:
Intermittent Fasting Reduces Body Fat But Exacerbates Hepatic Insulin Resistance In Young Rats Regardless Of High Protein And Fat Diets, The Journal of Nutritional Biochemistry, February 2017
Intermittent fasting (IMF) is a relatively new dietary approach to weight management, although the efficacy and adverse effects have not been full elucidated and the optimal diets for IMF are unknown.
We tested the hypothesis that a one-meal-per-day intermittent fasting with high fat (HF) or protein (HP) diets can modify energy, lipid, and glucose metabolism in normal young male Sprague–Dawley rats with diet-induced obesity or overweight.
The rats that fasted had higher serum glucose during an oral glucose tolerance test. They also had higher insulin levels. Both of these point to insulin resistance. They found as much. (HOMA-IR is a test for insulin resistance.):
HOMA-IR revealed significantly impaired attenuated insulin sensitivity in the IMF groups.
In conclusion, IMF especially with HF increased insulin resistance, possibly by attenuating hepatic insulin signaling, and lowered glycogen phosphorylase expression despite decreased fat mass in young male rats. These results suggest that caution may be warranted when recommending intermittent fasting, especially one-meal-per-day fasting, for people with compromised glucose metabolism.
In this diagram, when rats were allowed to eat ad libitum, when they wanted, their glucose gradually declined after a meal. When they were on a fasting diet, their glucose stayed elevated.
Insulin resistance accompanies type 2 diabetes, the hallmark of which is high blood glucose. Where does the glucose come from when you’re fasting? Hormones break down glucose stored in liver and muscles and release it to the bloodstream. When those stores are depleted, say, during an extended fast or a low-carb diet, the body breaks down muscle for energy – which would exacerbate sarcopenia (age-related muscle loss).